Effect and Mechanism of Rare Earth Trifluoromethanesulfonate on the Thermal Stability of Polypropylene†

doi:10.7503/cjcu20180727

Abstract

Abstract:

The thermal degradation of polypropylene(PP) was a free radical chain reaction, in other words, free radicals were the primary cause of combustion and degradation. Rare earth trifluoromethanesulfonate [Yb(OTf)₃ and La(OTf)₃] can interfere degradation process of PP via capturing the free radicals, thus effectively improving the thermal stability of PP. PP composites filled with two kinds of rare earth trifluoromethanesulfonates were prepared via melt blending utilizing the free-radical trapping ability of Yb(OTf)₃ and La(OTf)₃ in this paper. The thermal-stability of PP was tested by thermogravimetric analysis(TGA), differential scanning calorimetry(DSC) and thermogravimetric analysis coupled to Fourier transform infrared spectroscopy(TGA-FTIR). The results showed that Yb(OTf)₃ and La(OTf)₃ could improve the thermal-stability of PP dramatically. Simply when the addition of Yb(OTf)₃ was 1%(mass fraction), the onset degradation temperature of PP was increased from 275 ℃ to 305 ℃, the temperature corresponding to the maximum rate of mass loss increased from 384 ℃ to 405 ℃, the oxidative induction time at 160 ℃ extended from 12.1 min to 43.0 min, and the enthalpy reduced from 1907 J/g to 483 J/g, respectively. Moreover, the onset degradation temperature, the maximum rate of mass loss, the oxidative induction time at 160 ℃ and the enthalpy of PP filled with 1%(mass fraction) La(OTf)₃ were 300 ℃, 409 ℃, 18.6 min and 633 J/g, respectively. The effect of La(OTf)₃ on the thermal stability of PP was weaker than that of Yb(OTf)₃. We tried to explain these differences and then propose the possible mechanism. Due to the combined action of anions and cations, Yb(OTf)₃ and La(OTf)₃ could improve the thermal stability of PP. For La(OTf)₃, the free radical trapping ability of trifluoromethanesulfonate and the coordination ability of rare earth ions played a major role. For Yb(OTf)₃, in addition to the above reasons, the high reactivity of rare earth ions also played a key role.

Key words: Rare earth trifluoromethanesulfonate, Free-radical trapping, Thermal stability of polypropylene

CLC Number:

O631

TrendMD:

RAN Shiya,SHEN Haifeng,LI Xiaonan,WANG Zilu,GUO Zhenghong,FANG Zhengping. Effect and Mechanism of Rare Earth Trifluoromethanesulfonate on the Thermal Stability of Polypropylene^†[J]. Chem. J. Chinese Universities, 2019, 40(6): 1333.

Figures/Tables 13

Fig.1 TG(A) and DTG(B) curves of PP/Yb in air a. PP; b. PP/Yb0.1; c. PP/Yb0.2; d. PP/Yb0.5; e. PP/Yb1; f. PP/Yb2; g. PP/Yb5.

Table 1 Detailed data obtained from TGA and DSC tests for PP/Yb

Sample	Air		160 ℃		180 ℃		200 ℃
Sample	T_5%/℃	T_max/℃	OIT/min	ΔH_d/(J·g^-1)	OIT/min	ΔH_d/(J·g^-1)	OIT/min	ΔH_d/(J·g^-1)
PP	275	384	12.1	1907	2.3	5534	1.0	6442
PP/Yb0.1	263	391	14.9	1353	2.5	3796	1.0	4970
PP/Yb0.2	271	398	20.6	958	2.6	2615	1.0	3932
PP/Yb0.5	289	397	30.4	718	4.0	2602	1.0	3262
PP/Yb1	305	405	43.0	483	7.4	1688	1.0	2187
PP/Yb2	314	420	36.0	314	5.0	1225	1.0	819
PP/Yb5	323	430	36.7	172	3.3	208	1.0	225

Fig.2 DSC curves of PP/Yb at 160 ℃(A), 180 ℃(B) and 200 ℃(C) a. PP; b. PP/Yb0.1; c. PP/Yb0.2; d. PP/Yb0.5; e. PP/Yb1; f. PP/Yb2; g. PP/Yb5.

Fig.3 TG(A) and DTG(B) curves of PP/La in air a. PP; b. PP/La0.1; c. PP/La0.2; d. PP/La0.5; e. PP/La1; f. PP/La2; g. PP/La5.

Fig.4 DSC curves of PP/La at 160 ℃(A), 180 ℃(B) and 200 ℃(C) a. PP; b. PP/La0.1; c. PP/La0.2; d. PP/La0.5; e. PP/La1; f. PP/La2; g. PP/La5.

Table 2 Detailed data obtained from TGA and DSC tests for PP/La

Sample	Air		160 ℃		180 ℃		200 ℃
Sample	T_5%/℃	T_max/℃	OIT/min	ΔH_d/(J·g^-1)	OIT/min	ΔH_d/(J·g^-1)	OIT/min	ΔH_d/(J·g^-1)
PP	275	384	12.1	1907	2.3	5534	1.0	6442
PP/La0.1	268	399	18.2	1560	3.8	2581	1.0	4635
PP/La0.2	283	406	23.7	924	3.3	2907	1.0	3516
PP/La0.5	296	414	28.5	616	5.8	2429	1.0	2716
PP/La1	300	409	18.6	633	4.1	1565	1.0	2250
PP/La2	303	425	18.6	623	2.7	1673	1.0	2593
PP/La5	301	423	16.7	445	3.2	1094	1.0	1978

Fig.5 TG(A) and DTG(B) curves of PP(a), Yb(OTf)3(b) and La(OTf)3(c) in air

Fig.6 FTIR spectra for Yb(OTf)3(a) and gases evolved from Yb(OTf)3 in air at 380 ℃(b), 410 ℃(c), 450 ℃(d) and 470 ℃(e)

Fig.7 FTIR spectra of total gases evolved from PP(A), PP/Yb0.5(B), PP/Yb1(C), PP/Yb2(D) and PP/La0.5(E), PP/La1(F) and PP/La2(G) in air

Fig.8 FTIR spectra of total gases(A), hydrocarbons(B), CO2(C), CO(D) and carbonyl compounds(E) evolved from PP/Yb in air at 2965 cm-1(B), 2357 cm-1(C), 2179 cm-1(D) and 1730 cm-1(E) a. PP; b. PP/Yb0.5l c. PP/Yb1; d. PP/Yb2.

Fig.9 FTIR spectra of total gases(A), hydrocarbons(B), CO2(C), CO(D) and carbonyl compounds(E) evolved from PP/La in air at 2965 cm-1(B), 2357 cm-1(C), 2179 cm-1(D) and 1730 cm-1(E) a. PP; b. PP/La0.5l c. PP/La1; d. PP/La2.

Fig.10 Changes of torque with processing time for PP(a), PP/Yb1(b) and PP/La1(c)

Fig.11 Activation energy versus RE mass fraction curves of PP/Yb(a) and PP/La(b)

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